| Description |
The soda ash that the ceramic industry knows is a refined fine granular white material. It is very pure (99%). Grades (light, natural and dense) differ in particle size and therefore bulk density but they have the same chemistry. The common ceramic use of soda ash is as a soluble deflocculant in ceramic slips and glazes. It works well in combination with sodium silicate to produce body slips that do not gel too quickly and whose rheology can be adjusted for changes in the hardness of the water. Higher soda ash proportions (vs sodium silicate) will produce a slip that gives a softer cast (stays wet longer). The total soda ash and sodium silicate amount should be tuned to create a slip that will eventually gel if left to stand. This thixotropic behavior will prevent it from settling. Sodium carbonate is also the preferred deflocculant for thinning glaze slurries.
Soda ash is not normally used as a source of Na2O in glazes because it is soluble. It is used as a key source of sodium in frits and glass. Its solubility makes it an ideal flux for Egyptian paste glazes.
Soda ash production goes back to ancient times. Today, it is refined from Trona ore in the US (where the largest deposits are found). The ore is calcined, dissolved and re-crystallized (other processes are used in other parts of the world). Soda ash is used in a very wide range of industries (glass is the single biggest user) so its chemical, physical and bulk properties are well understood and documented (General Chemical Industrial Products publishes an excellent booklet describing soda ash). |